1. Field of the Invention
The present invention relates to a twin-belt band conveyor.
2. Description of the Prior Art
The inventive twin-belt band conveyors are for transporting materials which would slide or roll off the conveying upper or lower belt on a steep conveying track of a conveyor band. In the case of bulk goods, the critical angle for conveying such goods on bands is between 30.degree. and 35.degree.. In general, it depends not only on the conditions possessed by the material to be conveyed by band but also on the band speed which, however, cannot be increased at will in view of the throwing effect of the band discharge. The danger of segregation plays a part here in many cases. This applies in particular to bulk goods and material to be conveyed of a similar consistency, including concrete. The inventive twin-belt band conveyor is suitable for conveying the above-mentioned materials because it can be operated at a selectable band speed which takes the danger of segregation into consideration accordingly but does not impair the conveying effect.
The inventive twin-belt band conveyor has a high degree of uniformity compared to bucket conveyors but is much less complicated technically and is contaminated much less by the material to be conveyed when it is sticky or viscous. This is due to the fact that the indentations formed between the guide means to form the conveying space on the steep tracks are straightened out again behind the steep track, so that the flat form of the conveyor belt is restored at least on the bends.
The invention starts from a known twin-belt band conveyor. The cover band and the conveyor band thereof are designed as smooth conveyor belts. The guide means consist of spaced spring roller assemblies which bend the two flat belts around the material to be conveyed brought together in the middle of the conveyor belt by its trough shape before the steep track, thereby forming a conveying space with a lentiform cross-section which is held together by the spring roller assemblies. The pulling effect is based on the inner friction of the material to be conveyed, which is increased by the inwardly directed pressure of the middle sections of each conveyor belt between the spring roller assemblies. This has an adverse effect on very sticky or mud-like or very fluid material to be conveyed. Furthermore, the inner friction is too small in particular in the case of mud-like material, even if considerably higher pressure is used, to achieve the small slippage between the material to be conveyed and the conveyor belt as is required for transport on steep conveying tracks. Furthermore, the more fluid, pourable or fine-grained the material being conveyed is, the more trouble-some the leaks in the conveying space are which occur between the spring roller assemblies forming the guide means. They are due to the uneven bearing pressure of the belt edges which are supposed to seal off the conveying space.
The invention is based on the problem of achieving a satisfactory constant transporting effect in a twin-belt band conveyor of the type assumed as being known, even in the case of sticky and mud-like or very fluid bulk goods, without having to use a band speed too high with regard to the danger of segregation.